A hydraulic amplifier may be generally regarded as a hydro-mechanical device in a which small-amplitude, low-force mechanical displacement of a member is used to provide a high response modulation in hydraulic power. The motion of the member may be caused by a suitable electro-mechanical device, such as a torque or force motor.
Such amplifiers are commonly used in electrohydraulic servovalves of the single-stage or two-stage type. In a single-stage or direct-drive servovalve, the hydraulic output of the amplifier communicates directly with the load. In a two-stage servovalve, the amplifier is typically used as a pilot-stage to selectively displace a second-stage valve spool relative to a body. In this case, the first-stage amplifier is used to create a pressure differential which is applied to the spool end areas. Displacement of the second-stage spool is used to vary orifices through which fluid may respectively flow from source to the load and from the load to the return. Thus, in a single-stage servovalve, the hydraulic output of the amplifier communicates directly with the load, whereas in a two-stage servovalve, the amplifier output is used to controllably move a spool to vary second-stage orifices through which fluid may flow with respect to the load.
In a single-stage servovalve, the movable member is typically a jet-pipe or a jet-deflector, such as representatively shown and described in U.S. Pat. No. 3,542,051 and 4,442,855. In a two-stage servovalve, the member may be a flapper arranged between two opposed nozzles, such as shown and described in U.S. Pat. No. 3,023,782 and 3,612,103. The aggregate disclosures of these patents are incorporated by reference herein insofar as a description of the structure and operation of such prior art devices is concerned.
In either case, pressurized hydraulic fluid continuously flows through the amplifier, and is available to do the commanded work. When the member is displaced off-null, the fluid parameters (i.e., pressure, flow, etc.) must be adequate for the intended purpose. However, when the member is returned to a null or centered position, fluid still flows through the amplifier. Thus, the amplifier consumes power while in a standby condition.
Therefore, it would be desirable to improve the efficiency of such a hydraulic amplifier by reducing the power consumed due to leakage flow when the member is in a null position, while continuing to afford adequate power capability for commanded off-null applications.